Elector

Elector is the fourteenth rank of the Imperial aristocracy, and the lower of the two Patriarchal ranks. Elector is less of a separate rank than it is an addendum to a previous one. The full title is actually Archduke-Elector Regnant, which ties back a bit into Imperial history.

History
In the Empire, the position of Emperor is not hereditary. That is, the title does not immediately pass to the Emperor's heir upon his death or abdication. Rather, the current Emperor is actually King of Terra, as King is the highest hereditary title. The next Emperor is always chosen through an election of the highest ranking members of the Empire left over after one has passed on.

Previously, the members who elected the new Emperor were those Archdukes who held seats on the Electoral College. The old and developed regions of space they ruled became Electorates as opposed to Archduchies, and the members became known as Archduke-Electors Regnant.

Currently, the law has been modified so that the Privy Council actually elects the next Emperor, and the Archduke-Electors Regnant lost their power in that regard. As this is no longer a hereditary power, Electorates are now more commonly known as Oversectors, though both names are technically correct. Elector is now a courtesy title granted to Archdukes who served on the Privy Council for a period of time, and the Oversectors are roughly the same size as a Sector (Archduchy) but consist of old, developed worlds that have been in human control for centuries, and thus are considered far more prestigious than other demenses. An example would be the Centaurus Oversector, which is an outcropping from the Local Cluster emanating from the Electoral Capital of Alpha Centauri, which was the first human colony outside of the Sol System.